1. Field of the Invention
The present invention relates to a fan blade axial and radial retention device.
2. Summary of the Prior Art
Axial and radial retention devices for fan blades have been proposed, for example in French Patent specification No. 2 345 605 which describes a device constituted by a wedge which is disposed between the root of a blade and the base of a groove provided in the rim of the rotor disc so as to apply the part of the root of the blade of dovetail form radially the furthest from the axis, against lateral teeth of the groove, the wedge being secured in the axial sense by a U-shaped bar which cooperates with corresponding notches provided in the root of the blade and in the teeth of the groove. This device also comprises a key interposed between the tip of the wedge and the front of the blade root.
During auto-rotation or rotation of the rotor at low speeds, the centrifugal force which is exerted on the blades is not sufficient to hold the roots of the blade applied simultaneously against the two inclined faces of the groove. At each turn, the blades pass from a support position on one of the sides of the groove to a support position on the other side. This gives rise to clicking and, which is more serious, a hammering effect which seriously damages the contact surfaces. If such damage is hardly acceptable for parts which are readily replaceable, such as the wedges, or the blades themselves, it is not the same for the rotor disc for which such damage is absolutely non-acceptable.
French Patent specification No. 2,029,000 discloses a radial securing device for a fan blade comprising a wedge of moulded elastomer material interposed between the root of the blade and the base of a groove or recess.
This insert of elastomer serves a damping role and reduction in the friction zones between the root of the blade and the groove; however, this device does not include a metallic element under stress exerting a substantial force against the blade root.
From French Patent specification No. 2,376,958 there is known a vibration damping device formed by an element of elastomer material in which is embedded an elastically-deformable metallic part. However, in this damping device, the thin steel sheet moulded into the elastomer does not in fact exert a force in the radial direction on the blades, but acts only to hold the damping device in contact with the plates.
The present invention has for its object a device serving to exert on the root of the blade, a substantial force in the radial direction and to improve the securing of the coverings applied on the bulb of the blade roots or on the flanks of the grooves of the disc.